I am looking for a -2.5 V negative output regulator

Discussion in 'The Projects Forum' started by simo_x, Jan 24, 2015.

  1. simo_x

    Thread Starter Member

    Dec 23, 2010
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    Hi all,

    I need a stable -2.5 V on a negative power supply rail so I am looking for a fixed -2.5 V negative regulator (same as 7905 for -5 V ).
    I found the LM2937-2.5 for positive 2.5 V, but I would need for a negative voltage output.

    Can you suggest me if there is a LM2937-2.5 negative equivalent ?
    Thank you in advance.
     
    Last edited: Jan 24, 2015
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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  3. ScottWang

    Moderator

    Aug 23, 2012
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    Try LM337 and adjust the output to 2.5V .
     
  4. simo_x

    Thread Starter Member

    Dec 23, 2010
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    I know the LM337 but I would like to avoid to adjust the output with the external resistors and having problems with tolerances etc.
    There is not a 'negative equivalent' for the LM2937 ? :confused:
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    You just using the pot to try and then using the fixed resistors to replace them.
     
  6. simo_x

    Thread Starter Member

    Dec 23, 2010
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    I already mounted a trimmer on my breadboard as well, where I am doing some testing before making the PCB. It's not so trivial to set it to -2.5 V..
    Maybe I have to try with 1 % resistors..
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    Sometimes you need to using 1% and different value of resistors in series with them.
     
  8. simo_x

    Thread Starter Member

    Dec 23, 2010
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    That's why I would like to avoid putting resistors in series etc..

    Actually, from datasheet, with R1 equals R2:

     -1.25 \left (2 \right ) + (120\,\Omega \times 100\,\mu\text{A}) \approx -2.5\,\text{V}

    I will try with 1 % resistors, I will buy these during the week. : )
     
  9. #12

    Expert

    Nov 30, 2010
    16,257
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    There are dozens of 2.5 volt regulators. If you would say what you need instead of what you want (an exact complement to an LM2937), you might some good results.

    Do you need -2.5 volts at 500 ma?
    Do you need 1/2% accuracy?
    Do you need it in a 3 pin package?
    Do you need it to survive 60 volt surges?
    What is the supply voltage?
    What is the actual current you need?
     
  10. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    I need a -2.5 V regulator with -5 V input from a 7905.

    The load current is not a problem, it will be very low, no more than 10 or 20 mA because I need it for reference voltage and for an op amp supply with high load to its output. TO220 package for the regulator is good enough.

    Thank you in advance.
     
  11. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    The LT3015-2.5 has a -2.5V fixed output.
     
    #12, atferrari, simo_x and 1 other person like this.
  12. simo_x

    Thread Starter Member

    Dec 23, 2010
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    6
    Thank you crutschow !
     
  13. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Finally I found at home 2 resistor of 100 Ohm 1 % tolerance. I tested the LM337 with them instead of using the trimmer and it works like a charm. :)

    Thank you all guys.
     
    Last edited: Jan 25, 2015
  14. crutschow

    Expert

    Mar 14, 2008
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    1% resistors will give a worst-case voltage error of ±1% plus the ±2 tolerance of the LM337 internal reference (at 25°C) or ±3% total output voltage error from nominal.
     
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